In a microwave-safe mug (about 10-12 oz), mix milk, vinegar, oil, and vanilla using a whisk or fork.
Add red food color and mix until the color is strong red.
Sift in flour, cocoa powder, baking powder, and salt. Add sugar and mix until smooth. Do not overmix.
Microwave the mixture on the default setting for 60-90 seconds. (Cooking time may vary; it usually takes 90 seconds.)
Let the cake cool for 15 minutes. You can put it in the fridge after 5 minutes to cool faster.
While the cake is cooling, mix the cream cheese frosting ingredients with a fork until creamy.
Spread the cream cheese frosting on the cake.
Serve and enjoy your red velvet mug cake!